Double alarm - making life difficult for burglars

7-36 — elektor july/august 1982 Most alarm systems can be divided into two main categories. They are normally activated by closing, or inter- rupting a circuit loop. One of these basic principles is used irrespective of the electronic method adopted, (micro-wave, infra-red, photo-cells, contacts etc.). Today"s burglar is not the simple- minded individual normally portrayed in comic strip cartoons. The professional certainly keeps up to date with the latest technological advances in alarm systems, and keeping him out is going to be difficult. Even part- timers unfortunately know something about electronics and alarm systems. Anyway the point is, that an average burglar can easily and quickly deter- mine what principle the system uses and at least try to deactivate it. This is sometimes made easier for the thief, wiring may present something of a problem. The circuit described here should pose a more difficult problem. It is intended to protect a single door, window or item of equ...